Permanent magnet chuck



April 1.1, 1944. SIMMONS 2,346,193

PERMANENT MAGNET CHUCK Filed Feb. 5, 1942 4 Sheets-Sheet 1 17 17 rif@ f[MN 15g/w 2 5 N s MNMN z//LY 1a *2- k 1 ao 5 n 4 5 3o 4,7 ai @e i@ @Pgli9 ze 37 S 37 5 a :1'9` g WW 1 L se 39 2`0 14 l 4010 40; I I

- Srwenfol: Frank L.. SLmmons B9 lm @H Herberc Cove# Gftorneg April 1l,1944` F, L. SIMMONS 2,346,193

PERMANENT MAGNET CHUCK Filed Feb. 5, 1942 4 sheets-sheet 2 fo j 40 56 105 E g 2 if y Frank L.5im,mon5

. 3B wihcss l l v NeT-ber? 6. Covey (Attorneg April 1l, 1944. F. 1SIMMONS PERMANENT MAGNET CHUCK 4 Sheets-Sheet 3 Filed Feb. 5 1942 NA QEEnventor Simm ons Frankl. Bg CQWF 9.

wirhes Herberc C. Covey VApril 11, 1944. F. L. slMMoNs PERMANENT MAGNETCHUCK 4 Sheets-Shea?l 4 Filed Feb. 5, 1942 Nfl nventor 51mm ons Frank LBg #Q Her-bevi Covers Patented Apr. 1l, 1944 UNITED STATES PATENT OFFICEPERMANENT MAGNET CHUCK Frank L. Simmons, Woonsocket, R. I. ApplicationFebruary 5, 1942,*Serial No. 429,675

13 Claims.

This invention relates to permanent magnet chucks and more particularlyto magnetic chucks in which the magnetism may be controlled to hold awork piece securely in position or to permit ready removal thereof.

A permanent magnet chuck of the type herein described comprises two setsof spaced, alternately arranged pole pieces of opposite polarity, whenmagnetically energized for holding work on the chuck, and one or morepermanent magnets operatively arranged in circuit with the pole piecesand work mounted thereon. In order to permit removal of the work, it hasbeen proposed to so arrange the magnets and associated parts thatmagnetic flux may be shunted out of the work by connecting the top polesof the magnet with both sets of pole pieces. This provision of a shuntpath however permits some of the pri- A mary iiux to permeate the workand still make its removal diicult. It has also been proposed to breakthe magnetic circuit between one of the magnet poles and its associatedpole pieces, but the direct or primary magnetic effect of the other poleand the secondary leakage flux still maintain such a holding power thatremoval of the work is likely to scratch its surface or that of theaccurately finished Work plate.

The primary object of my invention is to overcome such problems and toprovide a magnetic chuck f this general type in which the magnetic fluxis utilized eiliciently for holding the work piece, or alternatively theleakage and primary magnetic flux are removed from the work suflcientlyto permit ready release thereof.

It has also been proposed to make a magnetic chuck in which a pluralityof the magnets are mounted beneath the work plate with their polar facesin a reverse arrangement so that one magnet forms a return path for theux of another. The upper polar faces may contact magnetically withassociated pole pieces and the lower polar faces of the magnets may beconnected to form a circuit with the work on the work plate. If theupper magnet polar faces are moved so that each contacts with polepieces of opposite polarity and thus forms a shunt circuit for the flux,yet a strong flux goes through the work since the magnetic circuit hasnot been broken and all of the magnetic flux flows through the twopaths. If, moreover, the magnetic circuit should be broken between theupper polar faces of the magnets and their associated pole pieces,nevertheless the magnetic potential difference available for forcingflux through the work is concentrated near the upper terminal polarfaces of the magnets, and

this concentration of magnetic potential difference results insufficient leakage flux passing through the work to hold it withconsiderable force.

-A further object of my invention isto make a magnetic chuck of the typehaving one or more permanent magnets in which the magnetism is socontrolled that no magnetic potential difference will concentrate at orpolarize the pole pieces when the work is to be removed.

A still further object is to provide a permanent magnet chuck whichembodies provisions for removing the magnetic ux from the work whendesired and which is so constructed and arranged that a keeper may beapplied to the magnet poles when the chuck is not in use. Other objectswill be apparent in the following disclosure.

In accordance with my invention, I propose to make a permanent magnetchuck in which the polar faces of one or more magnets and associatedparts may be moved to break the magnetic circuit and to cause themagnetic potential difference to concentrate at points remote from thepole pieces. This may comprise a construction in which the two sets ofwork plate pole pieces of opposite polarity when energized or the upperpoles of a plurality of magnets of reverse polarity are magneticallyconnected together to depolarize the same, while the magnetic circuit isbroken at the opposite or lower magnet pole which thus becomespolarized. This is preferably accomplished by having the poles terminatein two sets of upper and lower polar faces which are operatively inmagnetic circuit with the as sociated sets of pole pieces when the chuckis on, but which are movable to inoperative or oi positions where eachof the upper polar faces may contact with and connect two adjacent workplate pole pieces, which are of opposite polarity when energized forholding lthe work, while the lower polar faces are isolated from theirpole pieces. In a chuck having a single magnet, a magnetic conductor ofhigh permeability provides a return path for the flux andthepolarization of the magnet unit at a point remote from the polepieces. In a chuck having a plurality of magnets mounted in reversepolarity arrangement, the construction is such thatthe upper spacedpolar faces of the magnets may be moved to contact with their associatedpole pieces and form a connecting shunt path, while the magnetic circuitis broken.

at the lower polar faces. In each type of chuck the magnetic potentialdiierence is caused to 'concentrate at the pole pieces to hold the workor at points remote from the pole pieces for removal of the work.

Various embodiments of this invention are illustrated in the drawings inwhich:

Fig. 1 is a vertical longitudinal section through a chuck having apermanent magnet provided with spaced polar faces at its top and bottomand arranged with a conductor for making a magnetic circuit with thework or alternatively for breaking the circuit and concentrating themagnetic potential difference adjacent to the lower magnet pole whileall of the work plate pole pieces are connected by the top polar facesof the magnet;

Fig. 2 is a top plan view, partly broken away, to show the magnet andassociated structure;

Fig. 3 is a, transverse vertical section through the magnet on the line3-3 of Fig. 2;

Fig. 4 is a fragmentary view similar to Fig. 1 in which the magnet hasbeen moved to a position in which the iron parts form a keeper for thepoles of the magnet;

Fig. 5 is a view corresponding with Fig. 1 in which the magnet has beenmoved to an ofi position;

Fig. 6 is a fragmentary sectional detail showing one manner of securingseparate ribs to the magnet body so as to form the desired spaced polarfaces;

Fig. 7 is a similar detail showing another way of securing the ribs to amagnet;

Fig. 8 is a longitudinal transverse section on the line 8-8 of Fig. 9 ofa chuck embodying a plurality of magnets in reverse polarityarrangement;

Fig. 9 is a top plan view of the work face of the chuck, partly brokenaway to show the arrangement of the magnets;

Fig. l is a transverse section on the line Ill-I0 of Fig. 9;

Fig. 11 is a similar transverse section on the line II-II of Fig. 9;

Fig. 12 is a fragmentary plan view of the bottom plate showing thearrangement of the Babbitt metal strips of the construction of Fig. 8and showing the magnets thereabove in dotted outlines;

Fig. 13 is a fragmentary under side plan view looking up at the bottomsof the three magnets as if the bottom plate were removed;

Fig. 14 is a top plan view of the assembly of the three magnets asremoved from the chuck casing;

Fig. 15 is aview similar to that of Fig. 8 in which the magnets havebeen moved to the olf or work removing positions;

Fig. 16 is a fragmentary detail corresponding with Fig. in which themagnets have been moved to a keeper position;

Fig. 17 is a fragmentary sectional detail showing a. plurality ofseparate narrow magnets in a vertical alternate arrangement in the onpositions;

Fig. 18 is a similar View showing the magnets in the off positions; and

Fig. 19 is a fragmentary vertical sectional view of a chuck of the typeshown in Fig. 1 in which separate slide plates are utilized to providethe spaced terminal polar faces of the magnet, which is immovablymounted.

A chuck embodying my invention may utilize a single large size permanentmagnet or a plurality of various shapes of magnets assembled to providethe required ux. The magnet may be made of suitable material, such as aferrous alloy known as Alnico and comprising aluminum, cobalt, iron andnickel. In the chuck shown in Figs. 1 to 5 inclusive, the magnet II) maybe shaped somewhat as a parallellepipedon, but, if desired, two or moreof the large magnets or a considerable number of small magnets inparallel or other arrangement may be connected together to act as aunit. Since a plurality of magnets act collectively as a single magnet,only one large magnet is shown in the drawings.

'Ihe work plate, which may be constructed as desired, is shown ascomprising a soft iron frame I2 having a series of parallel slots cuttransversely therethrough and forming the spaced cross bars I4. Softiron pole pieces I6 are assembled within these slots and held in placeby brazing at spaced points. Babbitt metal I1 is lled in the remainingspace, and the pole pieces are thus isolated from the cross bars andother parts of the plate I2. The pole pieces I4 and I6 preferably havethe same width. These iron inserts I6 form poles of one polarity whenenergized, herein termed the north pole pieces, and the cross bars andframe have the opposite polarity and are termed the south pole pieces.The Work plate I 2 may be suitably secured, as by cap screws I8, to endand side walls I9, and the latter are secured to the bottom iron plate20 by the same members. The end and side walls I9 of the casing maybemade cf iron or other magnetic metal or of non-magnetic material, suchas aluminum or brass, since the casing walls do not form a part of theprimary magnetic circuit.

The iron bottom plate 20 is connected magnetically with the frame I2 bymeans of soft steel or iron conductor plates 2l located at the oppositeends of the magnet together with soft steel or iron side plates 23.These conductor plates 2| and 23 have parallel plane top and bottomsurfaces which slidably t against the under side of the work plate I2and the top side of the bottom plate 20. 'Ihe magnet, or a pluralitythereof if used, and the conducting members 2| and 23 are assembled as asingle rigid unit which is mounted for sliding on the bottom 20 of thecasing and in sliding contact with the under face portions of the workplate. Since the magnet alloy is very hard, it cannot be readilymachined or drilled. I prefer to make the connections by casting themagnet with cores to form openings therethrough which may besubsequently ground to provide smooth surfaces, after which soft steelplugs are driven into the openings and then drilled out to form thebushings 25. The brass rods 26 are tted into these bushings, and theirouter ends carry nuts 21 located within recesses in the side conductorbars 23 which serve to clamp the side bars tightly against spacer blocks28 of brass or other nonmagnetic material and thus hold the magnet andthe plates 23 in a rigid assembly. The end conductor plates 2I are alsosecured to the side plates 23 by means of cap screws 29. A brass bushingwith an enlarged head 30 ts within a hole in each of the end plates andthe head 39 separates the end of the magnet from the conductor plates2I. A set screw 3l threaded into the left hand bushing 30 may be used toforce the magnet into tight engagement with the bushing 30 at theopposite end, thus making a very strong and rigid structure. It is to benoted that the side members 23 contact only with the side portions ofthe frame I2 and the cross bars I4, and they do not touch the north poleinserts I6, as shown particularly in Fig. 3. The north pole pieces I6flare outwardly beyond the sides of the magnet so as to provide a widework face, and the Babbitt metal parts I1 between the inserts I6 and thesouth pole cross ribs |4 are shaped accordingly.

A primary feature of this invention involves breaking the magneticcircuit between the lower south pole and its associated pole pieces.`For this purpose, I may utilize a construction in which the lower orsouth pole portion of the magnet isv shaped to provide a plurality ofnarrow ribs 36 which extend across the magnet and are equally spaced.The ribs have a width somewhat less than that of the cut out portions 31between them. The lower faces of these ribs, which constitute the southpolar faces of the magnet, are flat and lie preferably in the same orparallel planes. The bottom plate 20 of the chuck is also provided withspaced ribs 36, the tops of which form flat plane contact surfacescoextensive in area with the south polar faces of the ribs 36. Theseribs 38 may be formed by casting, milling, or otherwise cutting outparallel grooves in a fiat plate, and these grooves may serve as airgaps between the ribs, but they are` preferably filled with non-magneticmaterial 39, such as Babbitt metal. These non-magnetic inserts 39 arecoextensive in width with the air gaps 31 between the ribs 36 of themagnet, but are longer as shown in Fig. 3. The upper surfaces of theinserts 39 preferably lie in the same plane with the upper contactsurfaces of the ribs 38, s that the magnet may slide readily on thelower plate. The ribs and non-magnetic inserts are, therefore, such thatthe south polar faces of the magnet may contact fully with the Contactsurfaces of the ribs 38, or they may be moved to contact fully with thenon-magnetic material 39 and thus be isolated from the work plate.Hence, by moving the magnet longitudinally from the position of Fig. 1to the position of Fig. 5, the south polar faces are moved from anoperative magnetic circuit to an inoperative position where they arefully isolated from the south pole members of the work plate.

A further primary feature of this invention involves magneticallyconnecting the pole pieces of the work plate, when the south polar facesare insolated from the work plate and the magnetic circuit is broken asabove described, so as t0 eliminate the magnetic potential differencebetween the pole pieces of the work plate and to remove the flux fromthe work. This is accomplished by shaping the upper portion of themagnet, as illustrated in Figs. 1 to 5 inclusive, so as to provide a setof north polar ribs 4D, the top surfaces of which lie preferably in thesame plane so that they may slidably contact with the exposed underfaces or contact surfaces of the plate I2 and the pole pieces I4 and I6which lie also in that plane. The ribs 40 are arranged like the ribs 36across the magnet and they are separated by spaces 4I which arecoextensive in width with the south pole pieces I4 and the nonmagneticisolating material I1 which separates the two sets of pole pieces. Theribs 40 have the same width and length as the pole pieces I6, but theyhave double the width of the south polar ribs 36. The two sets of ribsare so arranged that, when the lower ribs 36 make full magnetic contactwith the bottom plate 20, the north polar faces of the ribs 40 likewisecontact only but fully with the under contact surfaces of the north polepieces I6. When the ribs 36 are moved to their inoperative positions, asshown in Fig. 5, then each top polar rib 40 will contact with both thesouth and the north pole pieces I4 and I6 that are adjacent. This servesto connect the pole pieces of the work plate and to remove the magneticflux from the work at the same time that the magnetic circuit is brokenat the lower south polar faces of the magnet. This arrangement makes itpossible to remove the work easily.

In this construction, the frame comprising the conducting plates 2| and23 is rigidly secured to the magnet and slides therewith in contact withboth the upper and the lower plates. The side plates 23 are always incontact with the frame I2. The top end of the right hand end plate 2|makes a continued sliding contact with the under side of the south polework frame I2. The top face of the left hand plate 2| is howeverarranged to overlap the adjacent Babbitt material I1 when the chuck isin the off position and thus aid in connecting the frame with theadjacent north pole piece I6. At the same time, the right hand end rib4|) overlaps the adjacent Babbitt metal I1 and contacts with the plateI2 and the adjacent pole piece I6. The two end plates 2| are cut away attheir bottoms, as indicated in Figs. l and 5, so that when the magnetand the plates are moved toward the right, these plates wfll contactonly with the Babbitt metal inserts 39. Thisl prevents any magneticconnection from the north pole piece I6 to the bottom plate throughthose end walls and the flux concentrates on opposite sides of thenon-magnetic inserts 39.

The frame plates 2| and 23 give the shortest possible path for the fluxto travel from the lower south pole of the magnet to its associated polcpieces, and this materially increases the magnetic force applied to thework over that which would be hadif the return path were made throughthe casing. Although the casing may be made of non-magnetic material,such as aluminum, it is now feasible to make this casing of iron or softsteel and thus provide a path for the leakage flux. As shown in Fig. 3the side walls I9 contact only at their central portions with the middleparts of the conducting plates 23, and thus form sliding surfaces whichguide the magnet and iron frame assembly in its sliding movement. Theprimary magnetic flux takes the shortest possible path through theconductor frame made of plates 2| and 23 from the associated pole piecesI4 to the lower magnet pole. When the magnet and frame are moved to theoff position, the magnetic potential difference concentrates beneath theunder sides of the Babbitt metal inserts 39 in the bottom plate and onthe south polar faces 36 of the magnet and the work plate is devoid ofholding power.

The permanent magnet may be moved relatively to the associated polepieces and the lower contact surfaces by suitable power or manuallyoperated mechanism. A simple construction as shown in Figs. 1 and 2comprises a short shaft 45 having an enlarged head 46 suitably mountedin a bearing on the side wall I9 of the casing for rotation therein. Theenlarged head 46 has a pin 41 arranged eccentric with and axiallyparallel to the shaft. A handle 48 is connected to the shaft and soarranged that revolving the handle serves to move the pin through anarc. The pin 41 is slidably inserted in an elongated slot 49 in the endof the brass member 50 which has a screw threaded end 5| threaded intothe right hand bushing 3|), as shown in Fig. l. Hence, by suitablyrevolving the handle, the permanent magnet may be moved from theoperative position of Fig. 1 to the inoperative position of Fig. 5.

The permanent magnet may be shaped by casting or by any other suitableoperation to provide the north and south polar ribs. In the form shownin Fig. 1 the ribs are indicated as integral with the body of themagnet, and this structure may be obtained by casting the magnet in theshape indicated and then grinding the outer faces of the ribs. I mayalso form the polar ribs of soft iron or other suitable magnetic metalwhich may be readily ground or otherwise machined to provide therequired smooth faces. That is, each rib 4|] and/or 36 may be initiallyshaped as a separate bar of soft iron or steel which is later attachedto the magnet. For example, it may be made substantially integral withthe body Ill of the magnet during the operation of casting the Alnicometal. One manner of securing the bar in position is to provide it withone or more pins 54 of suitable shape, such as one having an enlargedhead 55 (Fig. 6), which is driven into place in a hole in the rib andthere fastened by riveting. The Alnico metal may be cast in positionaround these pins and in contact with the under faces of the suitablysupported ribs. In the form shown in Fig. '7, the ribs may be formed ofseparate soft iron or steel bars which are secured to the topsubstantially plane face of the magnet Ill by welding metal 56. Variousother expedients may be adopted for securing the ribs 36 and 40 inposition.

This invention may also be employed in a permanent magnet chuck having aplurality of magnets mounted in a reverse polarity arrangement so thatone magnet forms a. return path for the flux from another. Oneconstruction is shown in Figs. 8 to 16 inclusive. That arrangementcomprises at least two and preferably three or more permanent magnets,which may be of the general shape and structure above described. In theform shown, the central magnet 60 is mounted so that its north polarface, for example, is at the top and two outer magnets 6| are arrangedin a reverse polarity so that their south polar faces are at the top.The central magnet is shaped to provide the narrow polar ribs 62 at itsbottom and the outer magnets have the narrow ribs 63 at their bottoms.The central magnet has the wide polar ribs 64 at its top and the outermagnets have the wide ribs 65 at their tops. The lower ribs 62 and 63 ofthe magnets are arranged in with contact surfaces on the upper portionsof spaced ribs 66 formed by cutting or casting parallel grooves in thebottom plate 61. The ribs 66 are coextensive in width with the lowerpolar faces of the ribs 62 and 63 of the magnets. The spaces 68 betweenthe ribs 62 and 63 of the magnets are also coextensive in width with theBabbitt metal inserts 69 mounted in the spaces between the lower ribs66, but these inserts may extend continuously across the bottom plate asshown in Fig. 12. The polar faces of the under ribs 62 and 63 ofthemagnet sare arranged in aligned sets as shown in Fig. 13, which is aview looking up at the under faces thereof, while the top polar faces ofthe upper ribs 64 and 65 are out of alignment as shown in Fig. 14. Atthe tops of the magnets, the ribs 64 and 65 are of the same width andeach is coextensive in width with the associated pole piece of the workplate; and the spaces between these ribs are coextensive with the widthof the other pole piece and the Babbitt metal 13 that isolates the southpole pieces 12 from the north pole inserts 19. The

work plate may be made as above described with reference to Figs. l to 5inclusive in which the south pole frame 14 has parallel slots cuttherethrough and the north polar pieces 10 are brazed therein and isolatedfrom the frame and cross bars 12 by the Babbitt metal 13 and brassbrazing.

The top polar faces of the ribs of the outer magnets slidably contactwith the under sides of the south pole bars 'I2 and the frame 14 at thesame time that the top polar faces of the central magnet also contactwith the pole pieces 10, so that when in the positions of Fig. 8 thechuck is "on and ready to hold the work piece. In that on position themagnetic ux from the central magnet passes upwardly through its polarfaces into the associated north pole pieces 10, thence through the workand back through the south pole pieces and top ribs 65 of the outermagnets and then to the lower ribs 63 and bottom plate 61 and backthrough the lower ribs 62 of the central magnet, thus making a fullcircuit.

As shown particularly in Figs. 10 and 14, the three magnets areconnected together so that they may be moved as a unit. In thisarrangement, the central magnet 60 is shorter than the two end magnets6| and the latter are connected at their ends by two plates 16 of softwrought iron. The two outer magnets are preferably cast by coring toprovide aligned holes which are filled with soft steel plugs and thelatter are then bored out to form steel bushings 11. A screw 18 is thenfitted into this bushing and threaded into a tapped hole in the plate16. The central magnet 60 is spaced from the outer magnets by brassspacers 80. The three magnets are held together by means of brass rods8| suitably secured in steel bushings 83 tightly fitted within the outermagnets and further steel bushings 84 tted within the central magnet.Adjusting nuts 85 on the brass rods serve to draw the parts togetherinto a rigid structure. Two brass bushings 66 are likewise mountedwithin central openings in the two end plates 16, and their enlargedheads 81 are located between the steel plates 16 and the end of thecentral magnet. A set screw 88 in the left hand bushing 86 forces themagnet toward the right into a rigid contact with the flared portion 81of the bushing 86 and thus holds the parts immovable relatively to eachother.

The assembled magnets may be moved by the same arrangement as abovedescribed which comprises a brass plate 99 (Fig. 8) having a threaded`end 9| screw threaded into the right hand bushing 85. A verticalelongated slot 92 carries the end of a pin 93 which is eccentricallymounted on the head of a shaft 94 carried by one of the side walls ofthe casing and operated by the handle 95. The end plates 16 are cut awayat their bottoms, as shown in Figs. 8 and 15, and the Babbitt metalinserts 69 are so arranged that when the magnets have been moved througha maximum distance toward the right the bottoms of these iron plates 16will contact only with non-magnetic material and thus the circuit willbe broken through these plates.

The top work plate 14 and the bottom plate 61 may be spaced by means ofend and side walls 98 and 99 of iron, aluminum, or other magnetic ornon-magnetic iiate'rial, and the parts are connected by set screws |00suitably mounted in aligned holes. the casing side walls do not form apart of the magnetic circuit. Hence, as is preferred, the

It will be noted that` walls 99 and 99 may be'made of soft iron. 'I'heside walls 99, are shaped, as shown in Fig. 11, to provide inwardlyprojecting ribs which contact with the outer magnets only at theircentral or equatorial portions so that these iron members do notinterfere with the magnetic action of the chuck. These inwardlyprojecting ribs |0| form slideways for guiding the magnets and holdingthem in correct position. The side wall 99 contacts onlyl with the southpole frame of the work plate as shown clearly in Fig. 10. The walls 98and 99 serve a very useful purpose by cooperating with the plates'16 toform a shield for stray magnetic ux. The magnetic shield does not carrythe primary ilux because the magnets themselves form return pathstherefor.

Narrow magnets may be substituted for the massive type described above.This is illustrated dia-grammatically in,Figs. 17 and 18 in which aset'of slidably mounted, narrow and vertical magnets |02 and |03 havetheir north and south poles in alternate arrangement as shown by theletters N and S. The tops of the magnets are coextensive in area withthe north and south pole pieces of the work plate, which may be madeashabove described. The top north polar faces of the magnets |02 contactwith the iron linserts |04 of the work plate, and the top south polarfaces of the magnets |03 contact with the iron cross bars of the workplate. The pole pieces are separated by the Babbitt metal |06. Themagnets are likewise isolated by Ibrass strips |01 suitably securedtherebetween, as by means of bolts running through the assembled magnetsand strips, so that the parts may be moved as a unit. The iron bottomplate |09 of the chuck is cut away to provide spaced ribs `I09 and thespaces therebetween are filled with Babbitt metal ||0. If desired, thebottom plate may be suitably isolated from the work plate, as by meansof aluminum side walls. The magnets are cut away at their bottoms sothat their lower polarhfaces I|| are coextensive in area with the topsof -the ribs |09 of the lbottom plate. The Babbitt metal inserts ||0between the ribs |09 are wider than those ribs and coextensive with thespaces between the bottom narrowed poles of the magnets. Thesedimensions are such that when the magnets have been moved toward theright to the positions indicated in Figure 18, then the bottom polarfaces I l of these magnets will contact wholly with the Babbitt metaland each of the magnets will be fully isolated from the bottomV plate,while at the same time the top poles of the magnets will straddle theinsulation |09 between the pOle pieces and connect as a parallelepipedonand it may be provided with either one of the top or bottom sets of ribsillustrated in Fig. 1 while the other set is located in a slide bar asillustrated. In the preferred construction, there are two slide barswhich provide all of the terminal polar faces for the magnet or magnets.As shown, the work plate may have the north pole` serts ||4 mounted inslots `therein and separa d from the south pole cross bars ||5 by meansof Babbitt metal I5. The under faces of the cross ribs ||5 and the ironinserts ||4 are in the same plane. A brass slide plate I8 is mounted forsliding on the plane` top of the magnet in contact with vthe under faceof the work plate. This plate may be made of brass cut out to provideopenings within which iron inserts |20 are mounted. The iron insertshave plane top and bottom faces and are shaped to make full magneticcontact with the top of the magnet and with the under contact surfacesof the associated pole pieces. The brass and iron parts are so shapedthat the brass portions in the on" position of the magnet, extend whollybeneath the south pole ribs ||5 and the associated Babbitt metal stripsH6. The top of the magnet terminates in the polar faces of the tops ofthe iron inserts |20 which contact fully with the north pole inserts||4. These north pole inserts |20 are coextensive with the areas of theunder sides of the north pole pieces ||4. Similarly, another brass slideplate |22 is provided beneath the magnet. This plate has slots crosswisethereof within which are secured the iron inserts |24. These inserts arearranged to contact in the on position with the top exposed faces ofribs |25 on the bottom plate |26 of the chuck. These ribs |25 areseparated by inserts of Babbitt metal the same as above described.Various other modifications and arrangements may be made in the chuckconstruction, provided the primary features of this invention areincorporated therein so that the top poles of the magnets may be movedto connect adjacent pole pieces of the work plate while the bottom polesof the magnets are fully isolated from each other.

In view`of the above explanation of the invention, it will beappreciated that the magnets may terminate in polar faces on membersthat are not integral with the magnet but are in full magnetic contacttherewith. 'This issimply illustrated in Fig. 19, which represents amodication of the Fig. 1 construction, wherein the spaced polar facesare located on separate iron members that are sldable relatively to astationary magnet. The magnet I|2 may be shaped by an associated handle.

|21 which are substantially coextensive with the portions |28 of thebrass plate and are materially wider than the iron inserts |24, so thatwhen the slide |22 is moved toward the right the iron inserts maycontact wholly with the Babbitt metal |21 and thus fully break thecircuit at the bottom of the magnet and cause the lines of force toconcentrate there. In the on position, the iron inserts providing thepolar faces of the magnet make full contact with the magnetic parts ofthe work plate and the bottom plate, but when the slides ||9 and |22 aremoved toward the right the top iron inserts |20 will contact with boththe north and the south pole pieces while the lower iron inserts |24will con tact only with the non-magnetic Babbitt metal |21. Theoperation is therefore the same as that of Fig. l. The two slides ||8and |22 may be moved by a crank mechanism as above described. Theseslides are connected together by a cross arm |30 having threaded thereinthe cam part |3| having the slot |32'withn which rides the pin |33 thatis eocentrically moved A The magnet may be' held stationary by suitablemeans, such as a steel bushing |35 press fitted into the left hand endof the magnet and into which is tapped a screw thread for receivingabrass screw |36 carried in the iron end wall |31. That end wall |31 andside walls may be connected between the work plate and the bottom by`means of bolts |38 so that-the magnetic circuit may be made throughthese end walls and side walls.

The operations of the chucks will be apparent in view of the abovedescription. If the chuck has one or a plurality of magnets arranged asshown in Figs. l to 5 inclusive, then when the magnet i is in theposition of Fig'. 1 the flux traverses from the north polar facesthrough the ribs I8 and a work piece carried on the work plate andreturns through the cross ribs i4 and the work plate frame i2, theconductor plates 2l and 23 and the bottom plate 20. When the work is tobe removed, the magnet is slid to the position shown in Fig. 5 whererthesouth polar faces of the lower ribs t@ of the magnet are isolated fromthe associated south pole pieces i6. At the same time, the north polarfaces of the ribs 4U are brought into contact with the` under surfacesof both sets of pole pieces it and i6 which lie in one plane, and thuseliminates the magnetic potential dierence between the pole pieces andsets up a potential dierence between the bottom plate 2@ and the southpolar faces on the ribs 36 vof the magnet. Thus the work plate isdeprived of holding power by moving the effective polar faces of themagnet system to the bottom ofthe chuck and by interposing thereluctance of a gap in the circuit. The work may be readily removedbecause of of the resultant reduction in ux and because the ux does notenter the work to any material extent. When the chuck is not to be used,then the magnet may be moved part way so that the south polar ribs 36contact partially with the bottom plate 2o and the north polar faces ofthe ribs do contact partially with the south pole ribs id and northpoles i6. This provides a return path so that the parts form a keeperfor the poles of the magnet, as shown in Fig. 4.

The operation of the triple magnet construction is substantially thesame as that above indicated with reference to the Fig. 1 construction,since the magnets may be moved by means of the handle 95 to a positionwhere all of the top and bottom polar ribs make full contact with theassociated pole pieces and the spaced ribs of the bottom plate so thatthe magnetic lines of force pass through the work piece and the returnpath is formed by the magnets and bottom plate as indicated in Fig. 8.When the work is to be removed, the magnets are moved to the right asshown in Fig. l5 where the upper ribs 64 and 65 bridge the Babbitt metalspacers i3 and connect the adjacent north and south pole pieces and thusconnect the magnets to each other. At the bottoms of the magnets theribs 62 and 63 contact only with the Babbitt metal inserts 69 rand thusthe circuit is fully broken there. When the chuck is to be put away andnot used, then the magnets may be moved to an intermediate position asshown in Fig. 16 in which the lower ribs 62 andy63 of the magnet contactpartially with the cross ribs 66 of the bottom plate, while the upperribs 64 and 65 contact with both north and south pole pieces thusforming a return circuit so that the magnets have keepers appliedthereto.

The primary feature of each type ofA chuck, whether having one magnet,as in Fig. 1, or a plurality of magnets in a reverse polarityarrangement, as in Fig. 9, may be viewed as involving la magnet systemso constructed and arranged relative to the two sets of pole pieces inthe work plate that the magnetic potential difference may beconcentrated in the pole pieces for holding the work in position while acircuit of low reluctance is provided from the magnet poles to the polepieces; and then, when the work is to be removed, a gap of highreluctance is interposed in the circuit at a point remote from the workplate and the pole pieces are connected together magnetically, wherebythe energized polar faces of the magnet system are re-located on theopposite sides of the gap and the leakage ux does not enter the work. Ifthe magnetic circuit were not broken, there would be a strong eld andsome flux would enter and hold the work. Also, if the circuit werebroken only between the top of the magnet and its associated polepieces, then the magnetic potential difference would concentrate nearthe pole pieces and the leakage ilux would tend to hold the work.

This is exemplified in a two magnet system of reverse polarityarrangement. When the work is to be held in place, an armature is placedacross the bottoms of the magnets and the magnet tops are polarized, andwhen the work is to be removed the circuit is opened at the bottoms ofthe magnets and an armature connects their tops, so that the polarizedpolar faces are re-located at the bottom of the chuck away from thework.

It mayalso be observed that, in the construction of Fig. 1, the magnetis surrounded at its sides'and ends by a frame of wrought iron or softSwedish steel or other material that has a much higher permeability andlower reluctance than has the magnet, so that the frame may be made ofthin material and leave ample space for the magnet. This frame of highpermeability formed of the plates 2l and 23 remains in magnetic contactwith the south pole frame of the work plate for the different positionsof the magnet. When the magnet is in the on position, this frame formsthe primary return circuit for the flux. When the magnet is in the "oposition, the side and end plates 2i and 23 form a shield for leakageflux, and particularly if the stationary side walls of the casing aremade of non-magnetic material. It will also be noted that the end walls2l touch only babbitt at their bottom faces when the chuck is in the offposition and so do not form a direct shunt circuit for the flux.Similarly, in the Fig. 8 construction, the central magnet is surroundedby the two outer magnets and the end walls l. This outer unit contactsonly with the work plate frame i4 that surrounds the north pole piecesl0. Since the frame 'Hl of the work plate surrounds the north poleinserts, the center magnet needs to be only large enough to contact withits associated north pole inserts, while the two outer magnets are madelonger so that these outer magnets with their connecting cross plates 16will contact with the marginal portion of the south pole frame` as wellas the crossbars thereof thus distributing the magnetism quite uniformlyto all of the parts.

In view of the above disclosure, it will be appreciated that variousother modifications may be made within the scope of this invention andthat the above description is to be interpreted as illustrating thegeneral principles of the invention and the preferred embodimentsthereof and not as limitations on the claims appended hereto.

I claim:

1. A magnetic chuck comprising a work supporting plate having two setsof alternately arranged, spaced pole pieces having lower contactsurfaces separated by narrower gaps, a permanent magnet having upper andlower poles terminating each in a set of spaced polar faces, the upperpolar faces slidably contacting with the undersurfaces of all of thepole pieces, a bottom plate having magnetically interconnected, spacedcon- `tact surfaces separated by wider non-magnetic gaps, a conductorconnecting the bottom plate with one set of pole pieces. andmeans forslidably moving the polar faces in contact with the contact surfaces ofthe pole pieces and the bottom plate, said contact surfaces and facesbeing so arranged that each of the upper polar faces of the magnet maycontact solely with a single pole piece while each of the lower polarfaces is magnetically connected with the other set of pole pieces, oralternatively each of the upper polar faces may contact with twoadjacent pole pieces while each lower polar face is isolated from itsassociated pole piece or alternatively is connected thereto.

2. A magnetic chuck comprising a work plate having two sets ofalternately arranged, spaced pole pieces providing lower contactsurfaces of the same width which lie in an upper plane and are separatedby narrower non-magnetic gaps, a

bottom plate having magnetically connected contact surfaces in a lowerplane which are separated by wider non-magnetic gaps, a plurality ofslidably mounted permanent magnets having upper and lower po1ar faces inan alternate reverse polarity arrangement which slide in said planes,each of the polar faces having a width corresponding substantially withthat of its associated contact surface, the widths and spacings of saidfaces and surfaces being such that the lower polar faces may contactfully with magnetic material when each of the upper polar faces contactssolely with a single pole piece, and when each of the upper polar facesengages two adjacent pole pieces then each lower polar face may beisolated by the adjacent non-magnetic gap or alternatively engage acontact surface of the bottom plate, and means for slidably moving themagnets as a unit to said positions.

3. A magnetic chuck comprising a work plate provided with two sets ofalternately arranged, spaced pole pieces having lower exposed contactsurfaces separated by narrower non-magnetic gaps, a slidably mountedpermanent magnet having as its upper pole a set of ribs providing spacedpolar faces inI slidable contact with said surfaces and having as itslower pole` another set of ribs providing spaced polar faces, a bottomplate having a set of magnetically connected contact surfacescontactable with thel lower` polar faces and which are separated bywider nonmagnetic gaps, a conductor magnetically con,- necting thebottom plate with one set of pole pieces, each of the upper polar facesbeing substantially coextensive in width with an adjacent pole piece ofthe other set and being slidable to contact either with said pole piecealone or alternatively with two adjacent pole pieces, each of the lowerpolar faces being contactable 'witha contact surface of the bottom platewhen an upper polar face contacts solely with one pole piece oralternatively slidable to be isolated by a non-magnetic gap when anupper polar face contacts with two adjacent polev pieces, and meansassociated therewith for moving the magnet to form a magnetic circuitwith a work piece or alternatively to interconnect the pole pieces Aandbreak the magnetic circuit.

4. A magnetic chuck comprising a work plate having a frame and crossribs and a set of iron inserts Abetween and spaced from the ribs, saidribs and inserts forming two sets of pole pieces, and each having alower exposed contact surface, a vertically arranged movable permanentmagnet having upper and lower polar ribs, the upper ribs being arrangedto contact solely with said sur-f faces of the inserts or alternativelyto be moved into simultaneous contact with both sets of pole pieces, abottom plate having magnetically connected, spaced contact surfacessubstantially coextensive and contactable with said lower polar ribs andwhich are separated by wider nonmagnetic gaps, a frame of high magneticpermeability surrounding and movable with the magnet which connects thebottom plate with the work plate frame and ribs, and means associatedwith said parts whereby the magnet and frame may be moved so that thelower polar ribs engage said magnetic contact surfaces of the bottomplate when the upper polar ribs contact solely with the inserts oralternatively may be moved to a position where the lower ribs areisolated from the bottom plate when the two sets of pole pieces areinterconnected by said upper ribs.

5. A magnetic chuck comprising a work plate having two sets ofalternately arranged, spaced pole pieces, a bottom plate having spacedcontact surfaces separated by wider non-magnetic gaps, a centralpermanent magnet, two outer permanent magnets spaced therefrom at itsopposite sides in a reverse polarity arrangement relative to the centralmagnet, conductor plates magnetically connecting the ends of the outermagnets and contacting with said plates to transmit leakage flux, meanssecuring the magnets and conductor plates as a rigid movable unit, saidmagnets terminating in upper and lower spaced polar faces magneticallycontactable with said work pieces and bottom plate, and associated meansfor moving the magnets relative to said contact surfaces to positionswhere the upper polar faces interconnect pole pieces of 4oppositepolarity and the lower polar faces are isolated from the opposite magnetpole by said nonmagnetic gaps.

6. A magnetic chuck comprising a work plate having two sets ofalternately arranged, spaced pole pieces provided with lower contactsurfaces, a permanent magnet having upper and lower poles, the/upperpole terminating in movable, spaced-'polar faces which contact solelywith the lower surfaces of one set of pole pieces or alter natively aremovable to interconnect the two sets, and a magnetic conductor having acontact surface'arranged to contact magnetically with the lower magnetpole and complete a circuit with a work piece on the plate, said lowerpole being movable relative to the conductor so that it mayalternatively be isolated when the pole pieces are interconnected andthe magnetic potential difference maybe concentrated adjacent to saidlower pole when the Work is to be released.

7. A magnetic chuck comprising a Work plate having two sets ofalternately arranged, spaced pole pieces provided with lower contactsurfaces, a bottom plate having a magnetic contact surface connectedwith one set of pole pieces, and a movable permanent magnet unit havingspaced, upper, terminal polar faces arranged to contact solely with oneset of pole pieces and a lower polar face contactable withsaid surfaceon the bottom plate to form a circuit with a work piece, oralternatively the polar faces being movable to interconnect said polepieces and to isolate the lower polar face from the bottom plate so thatthe magnetic potential difference concentrates adjacent to said lowerpolar face when the work is to be released.

8. A magnetic chuck comprising a work plate having two sets ofalternately arranged, spaced pole pieces provided with lower contactsurfaces, a bottom plate having magnetically connected contact surfacesseparated by non-magnetic gaps, a plurality of magnets in a reversepolarity arrangement whose poles terminate in upper and lower polarfaces contacting magnetically with both sets of contact surfaces andforming a circuit with a work piece, and means for moving the polarfaces of the magnets relative to said surfaces to an alternative, workreleasing position, said upper polar faces interconnecting the polepieces in the alternative position while the lower polar faces areisolated by said gaps.

9.'A magnetic chuck comprising a work plate having two sets ofalternately arranged, spaced pole pieces separated by narrowernon-magnetic gaps, avbottom plate having magnetically connected contactsurfaces separated by wider nonmagnetic gaps, a permanent magnet whosepoles terminate in upper and lower spaced polar faces contactingoperatively with one set of pole pieces and said contact surfaces, meansproviding a gnetic path from the bottom plate to the othei` set of polepieces and means for moving the polar faces to alternative positions forreleasing the work, said faces and surfaces being so arthatthe upperpolar faces contact with and interconnect both sets of pole pieces andthe lower polar faces are isolated by the non tei-..1- gaps when in thealternative work releasing positions.

l0. A magnetic chuck comprising a work supporting plate having two setsof alternately ar= ranged, spaced pole pieces having lower contactsurfaces separated by narrower non-magnetic gaps, a bottom plate havingmagnetically connected but spaced contact surfaces separated by widernon-magnetic gaps, a plurality of permanent magnets whose polesterminate in upper and lower polar faces operatively contacting withsaid surfaces and fo a magnetic circuit with a workpiece on the workplate, and means for moving the polar faces relative to said surfaces toan alternative work releasing position, said contact surfaces and polarfaces being arranged so that the upper polar faces may be moved tointerconnect the two sets of pole pieces andthe lower polar faces may besimultaneously isolated by said gaps.

1l. A magnetic chuck comprising a work plate having two sets ofalternately arranged, spaced pole pieces provided with lower contactsurfaces separated by narrower non-magnetic gaps, a bottom plate havingmagnetically connected contact surfaces separated by wider non-magneticgaps, a movable permanent magnet having its poles terminating in upperand lower spaced ribs, the upper ribs being substantially coextensivewith and slidably contacting with only one set of pole pieces oralternatively engaging and interconnecting both sets, and the lower ribsbeing substantially coextensive with and engaging the contact surfacesof the bottom plate when a work piece is to be held or alternativelybeing isolated by said non-magnetic gaps when the pole pieces areinterconnected, and means for moving the magnet.

l2. A magnetic chuck comprising a magnetic bottom support, side walls, awork plate on the side walls having two sets of alternately arranged,spaced pole pieces, a permanent magnet movably mounted on said supportand having upper and lower poles, the upper poles terminating in spacedpolar faces slidably contacting with one set of pole pieces and thelower pole operatively contacting with the support, a separate conductorplate of high permeability connected closely to and movable with themagnet and slidably contacting with the bottom support and that part ofthe work plate which has a like polarity when energized and means tomove the magnet and conductor plate, said magnet being movable tn analternative position where one pole is isolated from its associated polepieces.

13. A magnetic chuck comprising a casing having a bottom plate providedwith interconnected magnetic surfaces separated by non-magnetic gaps, awork plate and side walls therebetween,

said work plate having two sets of alternately arranged, spaced polepieces, a plurality of slidable magnets in a reverse polarityarrangement whose poles terminate in upper and lower spaced polar facesoperatively contacting respectively with said pole pieces and saidsurfaces of the bottom plate and alternatively movable to be isolated bysaid gaps, a conductor plate of high magnetic permeabilityinterconnecting magnets of the same polarity arrangement and contactingwith the bottom plate and that portion of the work plate which has thesame polarity when energized and means for moving the magnets.

FRANK L. SIMMONS.

